The present invention relates to a servo control signal generation device for detecting a defect signal and a mirror signal, and an optical disk device using the servo control signal generation device.
When playing back an optical disk, dust which adheres to the surface of the optical disk or a scratch on the surface of the optical disk, if any, disturbs a servo signal and makes accurate servo control impossible. A transient response of servo control caused by dust or a scratch can be stabilized by generating a defect signal from an RF signal to detect a defect part such as the dust or scratch and causing hold operation of servo control over a defect time period. As a generation method of the defect signal, a method of using a top envelope of the RF signal is disclosed. See, for example, JP-A-10-21547.
In the optical disk device, a mirror signal can be used to count the number of crossing tracks in seek operation for moving an optical pickup in a disk radial direction to a desired address position on the optical disk. In tracking pull-in at the end of the seek operation, tracking brake operation for generating a tracking brake pulse by using a phase relation between the mirror signal and a tracking zero-cross signal and outputting only a drive signal that acts in a direction opposite to a movement direction of an objective lens from among tracking drive signals by using the tracking brake pulse is conducted. As a method for generating the mirror signal, a method using a bottom envelope of the RF signal is disclosed. See, for example, JP-A-2003-242658.
As for write once optical disks such as widely spread CD-R and DVD-R disks at the present time, a type in which the reflectance of a recording film after recording becomes lower than that before recording is typical. In contrast with such an optical disk, however, an optical disk in which the reflectance after recording becomes higher than that before recording is also proposed. See, for example, Japanese Patent No. 2512087 (JP-A-02-005238). Hereafter, optical disks of the type in which the reflectance after recording becomes lower than that before recording are referred to as High-to-Low media, whereas optical disks of the type in which the reflectance after recording becomes higher than that before recording are referred to as Low-to-High media.